Disease or Molting?

I'm new to owning chickens. One of my Barnevalder has started losing feathers around her head/neck. Is this moulting or does it looks like mites/other disease. I see no noticeable black flecks or eggs around base of feather. She has stopped producing eggs. Her sister Barnevalder has not started losing feathers yet.

High quality diet is important during this time of molt. Some folks use 22% game bird pellets/crumbles alone, or mixed with layer pellets/crumbles, but we should know animal proteins are superior to plant proteins. Buttermilk and fish are a good supplement twice a week during this time, and most chickens seem to like it. A couple ounces of buttermilk added to a pound of feed to make a wet mash is good. Giving some no salt or low salt tuna is good too. Just clean it up after they eat to avoid moldy spoiled remains from sitting out for them. Give a high quality vitamin supplement in the water like Avian Super Pack during this time as well. It will make the process of storing nutrients during this time much less stressful on the birds.